A brain aneurysm, also called an intracranial aneurysm, is an abnormal bulge or ballooning in a blood vessel supplying the brain. The weakened area forms a sac that fills with blood. Intracranial aneurysms can rupture and cause bleeding into the brain. Usually this occurs in the area between the brain and the surrounding membrane (the arachnoid), called the subarachnoid space, causing a subarachnoid hemorrhage. Subarachnoid hemorrhage resulting from a ruptured intracranial aneurysm occurs approximately 35,000 times per year in the United States.
Currently, intracranial aneurysms are treated by microsurgical clipping or endovascular coiling. In the latter, the goal is to prevent aneurysm rupture by inserting a thin wire into the aneurysm forming a coiled structure which blocks blood flow into the aneurysm. In some treatment paradigms, intracranial stents are used within the blood vessel to buttress placement of coils. Such stents serve as a mechanical scaffold in order to help contain the coil mass within the aneurysm dome.